The present invention relates to a diaphragm pump that performs a pumping action by deforming a diaphragm thereof.
Unexamined Japanese Utility Model Application Publication No. 7-14179 discloses a typical diaphragm pump. As shown in FIG. 5 that shows this conventional diaphragm pump, it includes a diaphragm case 91, a diaphragm 92 and a driver 93. The diaphragm case 91 includes a block 94 and a tension plate 98 fixed to the block 94. The outer peripheral portion 92a of the diaphragm 92 is held between the block 94 and the tension plate 98. A pump chamber 95 is defined by the diaphragm 92 and the block 94.
The driver 93 includes a rod 96 that is reciprocated by the operation of a drive source (not shown) such as an electric motor and a support portion 97 that connects the rod 96 to the center portion of the diaphragm 92. The support portion 97 includes a first support member 97a that is located on the surface of the diaphragm 92 on one side thereof, or upper surface as seen in FIG. 5, so as to face a part of the upper surface of the diaphragm 92 and a second support member 97b that is located on the surface of the diaphragm on the other side hereof, or lower surface in FIG. 5, so as to face a part of the lower surface of the diaphragm 92. The diaphragm 92 is held at its center portion by the support portion 97 between the first and second support members 97a, 97b. 
The diaphragm 92 is deformed or displaced in accordance with the reciprocation of the rod 96, thereby increasing and decreasing the volume of the pump chamber 95. During the suction stroke of the diaphragm 92, the volume of the pump chamber 95 is increased and a fluid is drawn into the pump chamber 95. During the discharge stroke, the volume of the pump chamber 95 is decreased and the fluid is discharged out of the pump chamber 95.
Meanwhile, in the above conventional diaphragm pumps, the diaphragm 92 is held at the outer peripheral portion 92a thereof by the diaphragm case 91 and at the center portion thereof by the support portion 97 of the driver 93. Thus, stress caused by this holding or compression is constantly applied to portions (held portions) of the diaphragm 92 that are held by the diaphragm case 91 and the support portion 97. Additionally, an excessive stress is concentrated to the above held portions of the diaphragm 92 and the boundary between the held portions and the non-held portion of the diaphragm 92 due to the tensile force caused by the deformation of the diaphragm 92. Since excessive load is applied to the diaphragm 92 as described above, the lifetime of the diaphragm 92 is shortened.
In addition to the above-described diaphragm pump in which the diaphragm is deformed directly by the driver as shown in FIG. 5, a diaphragm pump of the type in which a back pressure chamber is formed on the side of a diaphragm opposite to a pump chamber and the diaphragm is deformed by varying the pressure in the back pressure chamber is known. In such diaphragm pump, the outer peripheral portion of the diaphragm is held by the diaphragm case, so that the same problem as that described above has occurred.
The present invention is directed to a diaphragm pump that improves the lifetime of a diaphragm thereof.